U.S. patent application number 10/718463 was filed with the patent office on 2004-05-27 for cylinder head and crankcase manufacturing and assembly techniques.
Invention is credited to Bloemers, James L., Britt, Alan, Ford, Elmer R..
Application Number | 20040098860 10/718463 |
Document ID | / |
Family ID | 25462460 |
Filed Date | 2004-05-27 |
United States Patent
Application |
20040098860 |
Kind Code |
A1 |
Britt, Alan ; et
al. |
May 27, 2004 |
Cylinder head and crankcase manufacturing and assembly
techniques
Abstract
A method of manufacturing a cylinder head and crankcase for a
small engine. A crankcase and a cylinder head are cast to close
tolerances and include as-cast mounting flanges, which are
assembled in face-to-face contact by employing self-threading
screws. Bearing recesses are cast into the crankcase. The
cylindrical sidewalls of the bearing recesses are provided with
as-cast flutes and roller bearings are press-fitted into the
bearing recesses.
Inventors: |
Britt, Alan; (Talladega,
AL) ; Bloemers, James L.; (Nashville, AR) ;
Ford, Elmer R.; (Nashville, AR) |
Correspondence
Address: |
PEARNE & GORDON LLP
1801 EAST 9TH STREET
SUITE 1200
CLEVELAND
OH
44114-3108
US
|
Family ID: |
25462460 |
Appl. No.: |
10/718463 |
Filed: |
November 20, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10718463 |
Nov 20, 2003 |
|
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09932532 |
Aug 17, 2001 |
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Current U.S.
Class: |
29/888.06 |
Current CPC
Class: |
F02F 1/24 20130101; F02F
1/002 20130101; Y10T 29/49696 20150115; Y10T 29/4927 20150115; Y10T
29/49989 20150115; F02F 1/04 20130101; F05C 2201/021 20130101; F02F
1/242 20130101; Y10T 29/497 20150115; Y10T 29/49995 20150115; F02F
1/22 20130101; F02F 7/0053 20130101; F02B 2075/025 20130101; Y10T
74/2186 20150115; F02B 75/16 20130101 |
Class at
Publication: |
029/888.06 |
International
Class: |
B23P 011/00 |
Claims
1. A method of manufacturing a cylinder head for a small engine
comprising the steps of casting a cylinder head having an as-cast
cylinder chamber defined by a cylinder wall, an as-cast spark plug
aperture communicating with one end of said cylinder chamber,
cooling fins, an exhaust port extending from the cylinder chamber
to a first face on an exhaust post flange, an intake port extending
from said cylinder chamber to a second face on an intake port
flange, fastener openings in said first and second faces, a foot
flange having an as-cast mounting surface at another end of said
cylinder chamber, and having as-cast fastening apertures in said
foot flange; machining said cylinder wall to a predetermined
tolerance; and tapping said spark plug aperture.
2. A method of manufacturing a cylinder head according to claim 1,
wherein said as-cast spark-plug aperture is closed at one end by a
thin web and wherein said thin web is removed prior to tapping said
spark plug aperture.
3. A method of manufacturing a cylinder head according to claim 1,
wherein said exhaust port aperture and said intake aperture are
closed by thin webs forming portions of said as-cast cylinder
chambers and wherein said thin webs are removed when said cylinder
wall is machined.
4. A method of manufacturing a cylinder head according to claim 1,
wherein the flatness of the as-cast mounting surface of said foot
flange is 0.006 inch over its entire surface.
5. A method of manufacturing a cylinder head according to claim 1,
wherein said as-cast fastening openings in said foot flange are
cast to a perpendicularity of 0.002 inch with respect to the foot
flange mounting surface.
6. A method o f manufacturing a cylinder head according to claim 1,
wherein said as-cast fastening openings in said foot flange are
cast to within 0.006 inch of a true positional location on said
foot flange.
7. A method of manufacturing a cylinder head for a small engine
comprising the steps of casting a cylinder head having an as-cast
cylinder chamber defined by a cylindrical wall, an as-cast spark
plug aperture communicating with one end of said cylinder chamber,
cooling fins, an exhaust port extending from the cylinder chamber
to a first face on an exhaust port flange, an intake port extending
from said cylinder chamber to a second face on an intake port
flange, fastener openings in said first and second faces, a foot
flange having an as-cast mounting surface at another end of said
cylinder chamber, and having as-cast fastening in said foot flange,
said as-cast fastening openings in said foot flange being cast
within 0.006 inch of a true positional location on said foot flange
and being cast to a perpendicularity of 0.002 inch with respect to
the foot flange mounting surface, said as-cast mounting surface of
said foot flange being 0.006 inch over its entire surface; boring
said cylinder wall to a predetermined tolerance; and tapping said
spark plug aperture.
8. A method of manufacturing a cylinder head according to claim 7,
wherein said as-cast spark-plug aperture is closed at one end by a
thin web and wherein said thin web is removed prior to tapping said
spark plug aperture.
9. A method of manufacturing a cylinder head according to claim 7,
wherein said exhaust port aperture and said intake aperture are
closed by thin webs forming portions of said as-cast cylinder
chambers and wherein said thin webs are removed when said cylinder
wall is machined.
10. A method of manufacturing a cylinder head according to claim 1,
wherein apertures are cast in said fins, said apertures being
axially aligned with the fastening apertures in said foot
flange.
11. A method of manufacturing a cylinder head according to claim 1,
wherein apertures are machined in said fins, said apertures being
axially aligned with the fastening apertures in said foot
flange.
12. A method of manufacturing a crankcase for a small engine
comprising the steps of casting a crankcase having a crank chamber,
a crankcase connecting flange defining an opening to said crank
chamber, said crankcase connecting flange having an as-cast flange
mounting surface, and having first and second fastener openings
cast into said as-cast flange mounting surface, and threading said
openings with self-threading fasteners.
13. A method of manufacturing a crankcase according to claim 12,
wherein the flatness of the as-cast flange mounting surface is
0.006 inch over its entire surface.
14. A method of manufacturing a crankcase according to claim 12,
wherein said first and second fastener openings are cast into said
surface to a perpendicularity of 0.002 inch with respect to said
surface.
15. A method of manufacturing a crankcase according to claim 12,
wherein first and second fastener openings are cast to within 0.006
inch of a true positional location on said surface.
16. A method of manufacturing a crankcase according to claim 12,
wherein an O-ring groove is cast into said surface to surround said
opening, and wherein an O-ring is inserted into said groove.
17. A method of manufacturing a crankcase for a small engine
comprising the steps of casting a crankcase having a crankcase
chamber, first and second bearing recess at an end of said
crankcase chamber, each recess being defined by a cylindrical
sidewall having a plurality of rounded radially inwardly directed
flutes formed thereon, and pressing a roller bearing into each
recess.
18. A method of manufacturing a crankcase according to claim 17,
wherein the flutes are evenly spaced about the cylindrical
sidewalls and are separated by arcuate sidewall portions.
19. A method of manufacturing a crankcase according to claim 18,
wherein the flutes in said first bearing recess are offset an
arcuate distance with respect to the flutes in said second bearing
recess.
20. A method of manufacturing a crankcase according to claim 19,
wherein said arcuate distance corresponds to said arcuate
dimension.
21. A method of manufacturing a crankcase according to claim 20,
wherein the number of balls in said ball bearing do not equal the
number of flutes in a bearing recess.
22. A method of manufacturing a crankcase according to claim 20,
wherein the number of balls in said ball bearing are greater than
the number of flutes in a bearing recess.
23. A method of manufacturing a crankcase according to claim 20,
wherein there are eight balls in a ball bearing and seven flutes in
a bearing recess.
24. A method of manufacturing a crankcase according to claim 17,
wherein each roller bearing is pressed into each recess until it
seats on said toroidal base.
25. A method of manufacturing and assembling a cylinder head and
crankcase for a small engine comprising the steps of casting a
cylinder head having an as-cast cylinder chamber defined by a
cylinder wall, an as-cast spark plug aperture communicating with
one end of said cylinder chamber, cooling fins, an exhaust port
extending from the cylinder chamber to a first face on an exhaust
port flange, an intake port extending from said cylinder chamber to
a second face on an intake port flange, fastener openings in said
first and second faces, a foot flange having an as-cast mounting
surface at another end of said cylinder chamber, and having as-cast
fastener apertures in said foot flange; machining said cylinder
wall to a predetermined tolerance; tapping said spark plug
aperture; casting a crankcase having a crankcase chamber, a
crankcase connecting flange defining an opening to said crank
chamber, said crankcase connecting flange having an as-cast flange
mounting surface, and having first and second fastener openings
cast into said as-cast flange mounting surface; positioning the
as-cast mounting surface of said cylinder head foot flange in
face-to-face contact with the as-cast flange mounting surface of
said crankcase so that the as-cast fastening apertures in the
cylinder head foot flange are in axial alignment with the first and
second fastener openings of said crankcase flange mounting surface;
and fastening said cylinder head to said crankcase by threading
said openings and apertures with self-threading fasteners.
26. A method of manufacturing a cylinder head according to claim
25, wherein said as-cast spark-plug aperture is closed at one end
by a thin web and wherein said thin web is removed prior to tapping
said spark plug aperture.
27. A method of manufacturing a cylinder head according to claim
25, wherein said exhaust port aperture and said intake aperture are
closed by thin webs forming portions of said as-cast cylinder
chambers and wherein said thin webs are removed when said cylinder
wall is machined.
28. A method of manufacturing a cylinder head according to claim
25, wherein the flatness of the as-cast mounting surface of said
foot flange is 0.006 inch over its entire surface.
29. A method of manufacturing a cylinder head according to claim
25, wherein said as-cast fastening openings in said foot flange are
cast to a perpendicularity of 0.002 inch with respect to the foot
flange mounting surface.
30. A method of manufacturing a cylinder head according to claim
25, wherein said as-cast fastening openings in said foot flange are
cast to within 0.006 inch of a true positional location on said
foot flange.
31. A method of manufacturing a cylinder head according to claim
25, wherein apertures are cast in said fins, said apertures being
axially aligned with the fastening apertures in said foot
flange.
32. A method of manufacturing a cylinder head according to claim
25, wherein apertures are machined in said fins, said apertures
being axially aligned with the fastening apertures in said foot
flange.
33. A method of manufacturing a crankcase according to claim 25,
wherein the flatness of the as-cast flange mounting surface is
0.006 inch over its entire surface.
34. A method of manufacturing a crankcase according to claim 25,
wherein said first and second fastener openings are cast into said
surface to a perpendicularity of 0.002 inch with respect to said
surface.
35. A method of manufacturing a crankcase according to claim 25,
wherein first and second fastener openings are cast to within 0.006
inch of a true positional location on said surface.
36. A method of manufacturing a crankcase according to claim 25,
wherein an O-ring groove is cast into said surface to surround said
opening, and wherein an O-ring is inserted into said groove.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to single-piston, two-cycle gasoline
engines and more particularly, techniques for eliminating certain
prior art machining operations performed on cylinder head and
crankcase castings.
[0002] Current manufacturing techniques involve casting a cylinder
block and a crankcase using a die-casting process utilizing
standard casting tolerances that are relatively broad. The cast
cylinder and crankcase go through numerous machining steps to
arrive at the finished product, ready to be assembled together, and
with additional engine parts, into a completed engine.
[0003] Traditionally, a typical die casting process employs
"standard casting tolerances", which are known as "steel safe".
"Steel safe" means that the core pins that are used to produce
holes-in a part are on the high side of broad tolerances so that as
wear occurs on them, they would nevertheless remain in tolerance.
Die details that create the outside surface of the casting are
dimensioned on the low side of the broad tolerance so that wear on
the die allows the resultant part to remain in print tolerance.
This allows a die to produce large quantities of parts with little
attention paid to the dimensional integrity of the parts, resulting
in a low maintenance cost.
[0004] At least in the manufacture of cylinder blocks and
crankcases for single-piston, two-cycle gasoline engines, these
savings are illusory in that mating surfaces, such as the mating
surface between the block and the crankcase, must be machined.
Also, the broad tolerance core pin openings must be drilled and
tapped to receive the fasteners for these parts. Further, the
crankshaft bearing portal must be machined to a press tolerance and
machined to accommodate bearing locator snap rings. All of these
machining operations require labor and equipment costs, which
negate any savings in employing standard casting tolerances.
[0005] In addition to the cost factors involved in machining the
foot area of the cylinder head and the mating area of the crankcase
to ensure a proper seal, the machining operation itself contributes
to exhaust gas leaks in the casting. All aluminum die castings are
inherently porous. However, the initially chilled surface of the
casting provides a dense skin, which seals the porous interior of
the casting. When this skin is machined to provide precise gasket
mating surfaces between the cylinder block and crankcase, the dense
skin is removed and exhaust leakage is permitted through the gasket
area.
[0006] Analyzing the costs of the traditional machining operations,
including the costs of the machine tools, the labor involved in
operating the machine tools, the time loss due to the number of
steps involved, and the risks of poor quality due to potential
errors that the large number of operations required can cause led
to the realization that by requiring tighter tolerances on the die
mold and its components, one could decrease the total cost of the
manufacturing process despite the increased die mold and
maintenance costs and the decreased die mold life.
SUMMARY OF THE INVENTION
[0007] According to this invention, no machining operations are
required in the foot flange area between the cylinder block and the
crankcase. The die caster is required to hold tighter tolerances in
respect to flange flatness and surface finish, as well as the
fastener hole diameters and true positional location of those
diameters.
[0008] The preferred tolerances are:
[0009] Flange flatness=0.006 inch over the entire surface of the
flange
[0010] Perpendicularity of flange holes to the flange=0.002
inch
[0011] True positional location of the flange holes=0.006 inch
[0012] The cylinder block flange mates with a crankcase flange,
which also is die-cast to the same tight tolerances, and an O-ring
is provided in a groove in the crankcase flange. The O-ring and the
unmachined flange surfaces provide a reliable seal between the
flange surfaces and, since the fastener openings or holes are cast
to tight tolerances, self-tapping screws may be used to attach the
cylinder block to the crankcase, thus eliminating the need for
drill and tap operations.
[0013] This invention also provides for an improved bearing mount
for the crankshaft. The crankcase is die-cast, with bearing seats
having a plurality of radially inwardly directed flutes. The
bearings are press fitted into the seats. Even though press fit
tolerances are not as precise as machined tolerances, the as cast
flutes create spaces for material displacement during the bearing
pressing operation. The flutes also allow for a radial bending of
the surrounding casting material during the pressing operation
rather than a circumferential stretch, as occurs when the casting
is machined for a press fit.
[0014] Since a pair of roller bearing units are provided for the
crankshaft, a pair of bearing seats are provided with each bearing
seat extending inwardly from each end of the crankshaft portal in
the crankcase casting. The base of each bearing seat is defined by
an annular seat, which locates the bearing during the press fitting
operation. This eliminates the need for machined grooves and
locating clips in the driveshaft portal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a perspective view of a cylinder block according
to this invention;
[0016] FIG. 2 is a plan view of the cylinder block shown in FIG.
1;
[0017] FIG. 3 is an elevational view of the cylinder block, viewed
from the air-fuel intake side;
[0018] FIG. 4 is an elevational view of the cylinder block viewed
from the exhaust port side;
[0019] FIG. 5 is a cross-sectional view, the plane of the section
being indicated by the line 5-5 in FIG. 2;
[0020] FIGS. 6-9 are cross-sectional views that progressively
illustrate various machining operations performed on a cylinder
block according to prior art practices;
[0021] FIG. 10 is a flow chart illustrating the progression of
various prior art machining operations;
[0022] FIG. 11 is a flow chart illustrating the progression of
various machining operations according to this invention;
[0023] FIG. 12 is a perspective view of the crankcase according to
this invention;
[0024] FIG. 13 is a side elevational view of the crankcase;
[0025] FIG. 14 is an elevational view of the other side of the
crankcase;
[0026] FIG. 15 is a top plan view of the crankcase;
[0027] FIG. 15A is a cross-sectional view, the plane of the section
being indicated by the line 15A-15A in FIG. 15;
[0028] FIG. 16 is an elevational view of one of the crankshaft
bearings of the invention;
[0029] FIG. 17 is an elevational view of one side of the crankshaft
portal;
[0030] FIG. 18 is an elevational view of the other side of the
crankshaft portal; and
[0031] FIG. 19 is a view similar to FIG. 17 but showing the flutes
on the other side of the portal in phantom outline.
DETAILED DESCRIPTION OF THE INVENTION
[0032] Referring now to the drawings, and particularly to FIGS.
1-5, there is illustrated a cylinder block I 0 according to this
invention. The cylinder block 10 has an intake port flange 14, an
exhaust port flange 12, and a foot flange 16 at the bottom of the
cylinder block 10. The foot flange 16 is adapted to be connected to
a crankcase connecting flange, as will become apparent. First and
second fastener openings 18 and 19 are die-cast in the cylinder
block 10 under close tolerances. Fins 22 are provided on the
cylinder block 10 to cool the block during operation.
[0033] The cylinder block 10 is cast with a flange mounting surface
20 having an as cast flatness of approximately 0.006 inches. As
will become apparent, this provides a sealing surface that
eliminates the prior art machining step. Elimination of the
machining step on the surface 20 also eliminates the removal of the
as-cast skin, which selves as a seal against leakage through the
relatively porous interior of the casting.
[0034] The cylinder block 10 also is provided with axially aligned
openings 24 through the Fins 22 to provide tool access to the
fastener openings 18 and 19. The openings 24 are preferably as-cast
openings formed by core pins in the mold. Still further, the
cylinder block 10 is provided with a piston cylinder chamber 26, a
threaded spark plug opening 28, and scavenging ports 27. An exhaust
port 42 extends from the cylinder chamber 26 to a face 46 of the
exhaust port flange 12 of the block 10. Fastener openings 44 are
cast into the face 46 by mold core pins (not shown). The opposite
side of the cylinder block 10 is provided with an intake port 32
extending from the cylinder 26 to a face 36 of the intake port
flange 14 of the block 10. Fastener openings 34 are cast into the
face 36 by mold core pins (not shown).
[0035] Referring now to FIGS. 6-9, a series of prior art machining
operations that are accomplished at three separate machining
stations are illustrated. In FIG. 6, a die-cast engine block 10a is
die-cast to broad tolerances and positioned at a first machining
station. The piston block 10a is cast with a plurality of cooling
fins 22a, a piston chamber 26a, scavenging ports 27a, an intake
port 32a (FIG. 8), and an exhaust port (not shown). At the first
machining station, a flange mounting surface 20a of a foot flange
16a is machined to close tolerances as is indicated by the phantom
line in FIG. 6.
[0036] After the mounting surface 20a is machined at the first
machining station, the cylinder block 10a is transferred to a
second machining station (FIG. 7) where fastener openings 18a and
19a are drilled in the flange 16a and axially aligned access
openings 24a are drilled through the fins 22a. The fastener
openings 15a and 19a are tapped for fastening bolts (not shown).
Mounting holes 34a (FIG. 8) and mounting holes (not shown, but
corresponding to the holes 44) are drilled and tapped to
accommodate screws so that the intake manifold and the exhaust
manifold, respectively, can be mounted on the cylinder block 10a.
Further at the second machining station, a spark plug opening 28a
is drilled and tapped.
[0037] The cylinder block 10a is moved to a third machining station
(FIG. 9) where the piston chamber 26a is subjected to a boring
operation.
[0038] The sequence of the foregoing operations is illustrated in
FIG. 10. It should be appreciated that even though casting costs
are relatively low as a result of wide as cast tolerances, the
material handling and machining costs combine to eliminate any
savings in the casting operation. By requiring the die caster to
hold tighter tolerances, particularly with respect to the flatness
of the foot flange mating surface 20 and the fastener apertures, a
net savings results, even though casting costs are relatively
high.
[0039] The process according to this invention is illustrated in
the flow chart of FIG. 11. Initially, a die casting is produced
having tight tolerances, particularly with respect to flange
flatness and surface finish as well as fastener hole diameters and
the positional location of the diameters. The preferred tolerance
is approximately 0.006 inch for the mounting surface 20. The
perpendicularity of the fastener openings 18, 19, 34 and 44 to the
surfaces 20, 36 and 46 is approximately 0.002 inch. The true
positional location of the fastener openings 18, 19, 34 and 44 is
approximately 0.006 inch.
[0040] The casting is positioned at a single machining station
where the piston chamber 26 is subjected to a boring operation. The
spark plug hole or opening 28 is drilled and tapped and the axially
aligned fin openings 24 are drilled. The spark plug opening 28 is
substantially formed during the molding as is indicated in phantom
outline 28b in FIG. 5. To simplify the problem of a through core
pin in the mold, a thin web of material closes off the opening 28
in the as cast condition. It is this thin web that is removed
during the drilling step as indicated in FIG. 11. It is
contemplated that the drilling step may be eliminated by the use of
a through core pin, i.e., a core pin entering the mold surface,
which forms a top side 30 of the cylinder block. Similarly, the
fastener openings 18 and 19 are cast with thin webs of material 18b
and 19b, which are removed by a drilling operation as indicated in
FIG. 11. Further, the exhaust port 42 and the intake port 32 have
as cast thin webs adjacent the cylinder chamber 26. A separate
machining operation is not required since these webs are removed
during the boring operation. Additionally, it is contemplated that
the fin holes 24 need not be machined but may be provided in the
casting. Again, casting the holes 24 requires complicated core pin
placement in the mold.
[0041] Note that there has been a reduction in a number of
machining steps over the prior art. By comparing FIG. 10 and FIG.
11, it can be seen that the flange surface machining step of the
prior art has been eliminated, and the fifth and sixth steps are
simplified, because only the fins need be drilled and the thin web
49 of the first and second openings 18 removed. Also, by utilizing
self-tapping screws in the installation of the intake and exhaust
manifolds onto the intake port structure 14 and exhaust port
structure 12, respectively, there is no need to drill those holes
as in the fifth or to tap those holes as represented by the sixth
step. Further, the process is simplified by using only a single
machine where three had previously been employed.
[0042] The second aspect of the invention eliminates even more
machining steps by further increasing the features provided by the
casting process over that disclosed for the first aspect of tile
invention. The casting process of the second aspect of the
invention adds the following features, in addition to those listed
for the first aspect hereinabove.
[0043] The spark plug chamber 28 is cast fully open to the top side
30 of the cylinder. The fin holes 24 are formed by using pins in
the die casting process. In addition, first and second openings 18
through the flange 16 are completely open, so no web 49 is formed.
The tolerances on the flange surface 20 and the first and second
openings are the same as those identified above in the first aspect
of the invention.
[0044] By providing the aforementioned additional features during
the casting process, the machining steps shown in FIG. 11 can be
further reduced, so that the steps indicated by broken lines are
eliminated. This leaves only the steps described by solid lines
still necessary, as described below.
[0045] Referring now to FIGS. 12-19, there is illustrated a
crankcase 100, which is adapted to be attached to the cylinder
block 10. The crankcase 100 is cast to tight tolerances,
particularly in areas that are required to be machined according to
prior art practices. According to this invention, no machining
operations are required and the crankcase is assembled to the
cylinder block 10.
[0046] The crankcase 100 includes a crank chamber 102 into which a
piston rod (not shown) extends to drive a crank (not shown), which
converts the reciprocating motion of the piston rod to the drive
shaft (not shown) of a powered tool such as a chainsaw. The
crankcase 100 further includes a crankcase connecting flange 104
defining an opening 105 to the crank chamber 102 and having a
flange mounting surface 106 provided with first and second fastener
openings 108 and 110, which are adapted to be aligned with the
first and second fastener openings 18 and 19, respectively, which
are die-cast in the cylinder block foot flange 16. The openings 108
and 1 10 are also cast under the same tight tolerances as the
openings 19 and 20 so that the cylinder block 10 may be assembled
to the crankcase 100 by self-tapping fasteners (not shown) rather
than by threaded fasteners entering machined and tapped apertures
according to prior art techniques.
[0047] The crankcase 100 is cast so that its flange mounting
surface 106 has an as cast flatness of about 0.006 inches. This
provides a sealing surface that eliminates the prior art machining
step. Elimination of the machining step on the surface 106 also
eliminates the removal of the as-cast skin, which serves as a seal
against leakage through the relatively porous interior of the
casting.
[0048] A perimeter groove 1 12 is cast into the surface 106 and is
provided with an O-ring 114 (FIGS. 15 and 15A) preformed to the
outline of the groove 112. The O-ring 114 seals against the flange
mounting surface 20 of the cylinder block 10 when the cylinder
block 10 is assembled to the crankcase 100 as previously described.
To aid in this assembly step and to retain the O-ring 114 in place
during this operation, a tab 116 is provided on the O-ring 114 that
is received in a notch 118.
[0049] A bearing assembly is provided for the drive shaft, which
eliminates prior art machining steps in this area. Referring to
FIGS. 12-14 and 16-19, first and second bearing recesses 120 and
122 are cast at one end of the crank chamber 102. Each recess 120
and 122 is defined by cylindrical sidewalls 124 and 126 and by
toroidal bases 128 and 130, respectively. Each cylindrical sidewall
124 and 126 is provided with a plurality of rounded, radially
inwardly directed flutes 132 and 134, respectively. The flutes 132
and 134 are evenly spaced about the sidewalls 124 and 126 and are
separated by arcuate sidewall portions 136 and 138, each having an
arcuate dimension corresponding to the arcuate dimension of each
flute 132 and 134. As may be noted with reference to FIGS. 17-19,
however, the flutes 132 and 134 are mutually offset at a distance
corresponding to the aforementioned arcuate dimension.
[0050] A roller bearing 140 (FIG. 16) is press fitted into each
bearing recess 120 and 122. The provision of the flutes 132 and 134
allows for radial bending to occur between the contact areas of the
flutes, as opposed to circumferential stretch of the casting under
a heavy press fit. Also, the flutes allow for material flow between
the flutes during the pressing operation. The toroidal bases 128
and 130 form seats for the bearings 140 during the pressing
operation, thus eliminating the need for machined grooves and
locating clips in the drive shaft portal. The offset relationship
of the flutes 132 and 134 helps to minimize noise and vibration.
Also, to that end, the number of ball bearings in each bearing 140
is not equal to the number of flutes 132 or 134. In the illustrated
embodiment, there are eight ball bearings in each bearing 140 and
seven flutes 132 or 134 in each bearing cavity.
[0051] While the invention has been shown and described with
respect to particular embodiments thereof, those embodiments are
for the purpose of illustration rather than limitation, and other
variations and modifications of the specific embodiments herein
described will be apparent to those skilled in the art, all within
the intended spirit and scope of the invention. Accordingly, the
invention is not to be limited in scope and effect to the specific
embodiments herein described, nor in any other way that is
inconsistent with the extent to which the progress in the art has
been advanced by the invention.
* * * * *